The present invention relates to a drum commutator for electrical machines.
More particularly, it relates to a drum commutator which has an oscillating material drum and a plurality of commutator plates extending from its periphery and provided with a surface coating of carbon material and with a connecting lug for an armature winding of the electrical machine.
Drum commutators of the above mentioned general type are known in the art. They are utilized in wet electric motors in feed aggregates for aggressive liquids, for example in fuel pumps of motor vehicles. The surface coating of carbon material, for example graphite, which is resistant to the aggressive medium to be fed, protects the metallic surface of the commutator plates which are usually composed of copper. Otherwise, they would strongly oxidize and corrode during a current transfer with the resulting high and non-uniform voltage drop at the commutator.
Drum commutators of this type are disclosed for example in the German document DE-GM 89 07 045, page 2. Here the surface coating is formed as a graphite ring which is surface-treated on its inner surface and then soldered to the drum commutator. Then the graphite ring is slotted or in other words segmented so that a graphite coating is produced for the individual commutator plates. In this known plan commutator disclosed in this reference the commutator body composed of a synthetic plastic material is provided with a copper coating in which the commutator segments are formed. The plan surface of the commutator segments is provided correspondingly with a carbon coating which extends via form-locking holding means through the commutator plates into a corresponding recess in the commutator body and is anchored there.